JP2003145162A - Electrode for electrodialysis and electrodialysis method using the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for electrodialysis which has corrosion resistance and can be operated over a long time of period without replacement even when used for electrodialysis generating corrosive substances of high concentration, and an electrodialysis vessel. SOLUTION: An anode 7 supporting conductive diamond on the surface is used in the electrodialysis vessel 1. As the anode has high resistance against fluoride ions, it hardly deteriorates even when the fluoride ions in water 10 to be treated are moved to an anode chamber 4 and concentrated therein.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrode useful for electrodialysis, particularly for electrodialysis of water to be treated containing fluoride ions, an electrodialysis tank equipped with the electrode, and the electrode used for electrodialysis. On how to do.

[0002]

2. Description of the Related Art Air pollution caused by industry and household waste,
There is a concern that the deterioration of water quality in rivers and lakes will affect the environment and the human body, and there is an urgent need for technical measures to solve the problem. In a semiconductor manufacturing plant, various fluorine compounds are consumed in large amounts as a required elemental material and for the purpose of surface cleaning in a substrate and circuit manufacturing process, and a large amount of fluoride or its ion is discharged. Fluorine compounds are important synthetic products in the fields of resin industry, medicine, and agrochemicals, and the emission amount of fluoride ions due to these fluorine compounds increases. These fluorides or fluoride ions have a large environmental load, and there is an urgent need for measures to strictly adhere to the emission control values.

If the concentration of the fluorine compound is high, it can be recovered as CaF ₂ precipitate by reacting calcium hydroxide with hydrofluoric acid, but silicon metal is easily mixed in the fluorine-containing recovered material, which makes it valuable as a recycled raw material. There is a problem that is scarce. The current fluorine-based exhaust gas components are removed by combustion decomposition and partial recovery with a bag filter, followed by absorption of hydrogen fluoride with a scrubber, or addition of alkali such as sodium hydroxide to improve the recovery efficiency. ,
It is carried out by collecting wastewater containing 100 to 1000 ppm of fluorine and collecting the slurry from this wastewater by coagulation and coagulation. In this recovery method, the concentration of recovery is low, so it is preferable to concentrate it to about 10 to 100 times by using electrodialysis, but in the presence of fluoride ions, hydrofluoric acid is generated especially on the anode side, so that a stable electrode and cell are used. There was a problem that the material did not exist. Generally, there are ferrite, lead oxide, tin oxide, platinum, DSA, graphite, amorphous carbon (grassy carbon: GC), etc. as an anode that is an electrode for oxidation.
Examples of the cathode that is an electrode for reduction include lead, iron, platinum, titanium, carbon and the like. The material that can be used as the electrode substrate preferably has corrosion resistance in order to achieve a long life and prevent contamination of the treated surface, and it is desirable to use a valve metal such as titanium or its alloy as the anode power feeder. As the anode catalyst, it is desirable to use precious metals such as platinum and iridium and their oxides.

However, even if these expensive materials are used, it is known that when electricity is applied, the catalyst and substrate materials are consumed in accordance with the current density and the duration of the application, and are eluted into the electrolytic solution. An excellent electrode is desired. In particular, when a fluorine compound or its ion is present, it is difficult to perform stable operation because there are very few resistant electrode materials. Precious metals such as platinum are relatively stable, but they are insufficient in terms of yield and selectivity, and are expensive, which is an obstacle to practical use.

Diamond is promising as a semiconductor device, an energy conversion element, etc., since it has excellent thermal conductivity, optical transparency, high temperature and durability against oxidation, and in particular, its electrical conductivity can be controlled by doping. Is being watched. As an electrode for electrochemistry, Swain et al. Reported the stability of diamond in acidic electrolyte [Journal
of Electrochemical Society, Vol.141, p.3382 (199
4)], suggesting that it is far superior to other carbon materials. US Pat. No. 5,399,247 suggests that diamond can be used as an anode material to decompose organic wastewater. Foti reported that the decomposition mechanism of organic matter into carbon dioxide is promoted by a decomposition mechanism different from platinum in the electrolytic oxidation decomposition of organic matter [Electrochemical
and Solid-State Letters, Vol.2, p.228-230 (199
9)]. Further, Japanese Patent Application Laid-Open No. 2000-204492 discloses a fluorination reaction of an organic compound using an electrode made of semiconductor diamond.

[0006]

However, in the fields such as electrodialysis and electroplating, impurities are often present in the electrolytic solution. As described above, particularly in electrodialysis in which fluoride ions are present, hydrofluoric acid is present on the anode side. However, there is a problem that a stable electrode does not exist. The present invention provides an electrodialysis electrode capable of stably recovering the ions in a conventional electrodialysis, particularly an electrodialysis containing a low concentration of fluoride ions, and an electrodialysis method using the electrode. The purpose is to

[0007]

The present invention provides an electrodialysis electrode and electrodialysis tank containing conductive diamond as an electrode material, and further concentrates fluoride from electrolyzed water containing fluoride ions by electrodialysis. In the above method, conductive diamond is used as an electrode for electrodialysis.

The present invention will be described in detail below. In the present invention, conductive diamond is used for electrodialysis, and as a result, improvement of cell stability and acquisition of the target reaction product in high yield can be achieved. Conductive diamond is corrosion resistant and stable by itself against corrosive substances such as fluoride ions, and usually depends on the manufacturing method, but it is usually coated on the substrate as a dense layer, so it is a corrosive liquid. It is possible to almost completely prevent the corrosion of the substrate due to the permeation of. Electrodialysis is industrially used for concentration of salt from seawater, purification of drinking water, concentration of waste liquid, and the like. In an electrodialysis tank, cation exchange membranes and anion exchange membranes are installed alternately, and when a direct current is applied, the movement directions of ions in the electrolyte solution are reversed, and the electrolyte is concentrated and desalted from the electrolyte solution. It will be possible.

A plurality of ion exchange membranes can be arranged between the electrodes, but problems such as corrosion due to leak current occur as the cell voltage between the electrodes increases, so a bipolar plate is installed every 10 to 100 pairs. I often do it. There is a limiting current depending on the concentration and supply speed, and operation exceeding this limiting current causes a decrease in current efficiency, so the desalination rate is 10 to 90%.
It is preferable to adjust to the range of%. Further, it is desirable to sandwich a spacer having a large aperture ratio in order to prevent contact between the film and the electrode. When electrodialyzing a solution containing fluoride ions in such an electrodialysis tank, the fluoride ions, which are anions, are attracted to the anode and the concentration of fluoride ions in the anode chamber rises. Anodes such as ferrite and lead oxide that are commonly used in conventional electrodialysis tanks are likely to deteriorate. Therefore, in the conventional electrodialysis tank, the treatment of the solution containing the fluoride ion is premised on the consumption of the anode, and there is no means other than frequent replacement of the anode.

On the other hand, according to one embodiment of the present invention, an anode containing conductive diamond having resistance to fluoride ions as an electrode material can be used, and electricity of treated water such as wastewater containing fluoride ions can be used. Even if the treatment by dialysis is performed, deterioration of the anode hardly occurs, and electrodialysis can be performed for a long period of time without replacing the anode. Examples of the fluoride in the present invention include MF, M [BF ₄ ], M ₃ [AlF ₄ ]
And M ₂ [SiF ₆ ] (where M is a metal cation or a proton) and the like, and an anion in which at least one M is eliminated from these fluorides is a fluoride ion. In addition, electrodialysis may be used to treat solutions containing corrosive substances other than highly contaminated fluoride ions,
Even in that case, the electrodialysis tank and electrodialysis method of the present invention using conductive diamond as an anode are effective. Conductive diamond, which is an electrode material, is preferably formed on a current collector such as a metal. There is no problem if the current collector is a conductive material, but plates such as titanium, niobium, tantalum, silicon, carbon, nickel, and tungsten carbide, punched plates, wire nets, powder sintered bodies, metal fiber sintered bodies, etc. Can be preferably used.

An intermediate layer may be provided in order to improve the adhesion between the current collector and the conductive diamond and to protect the current collector. As the material for the intermediate layer, a carbide or oxide of the current collector material can be used.
Polishing the surface of the current collector or the intermediate layer contributes to the adhesion and increase of the reaction area. At this time, if diamond powder is used as nuclei to adhere to the surface of the current collector or the surface of the intermediate layer, it has the effect of growing a uniform diamond layer. Diamond electrode
Hot filament CVD method, microwave plasma CVD
Method, plasma arc jet method, PVD method, or the like. In addition to this, when using synthetic diamond powder under ultrahigh pressure, it is also possible to use a binder such as resin or ceramics, or fix the powder while forming an oxide by firing.

The hot filament method, which is a typical diamond electrode manufacturing method, will be described. Keeping organic compounds such as alcohol, which is a carbon source, in a reducing atmosphere such as hydrogen gas, the temperature at which filaments are generated by carbon radicals 1800-
Heat to 2400 ° C. Then, the power supply body and the electrode base body are arranged in the atmosphere so that the temperature range (750 to 950 ° C.) in which diamond is deposited is reached. At this time, the concentration of the organic compound with respect to hydrogen is 0.1 to 10% by volume, the supply rate is 0.01 to 10 liter / min, and the pressure is 2 kPa, depending on the size of the reaction vessel.
It is preferably -100 kPa. Diamond fine particles having a particle size of 0.01 to 1 μm are usually deposited on the electrode substrate. The thickness of the diamond layer may be adjusted by increasing or decreasing the operating time, and the thickness is preferably 0.1 to 50 μm, and preferably 1 to 10 μm for the purpose of preventing the electrolyte solution from entering the electrode substrate. Is particularly preferred. In the microwave plasma CVD method, the raw material is converted into radicals by a microwave having a frequency of 2 to 3 GHz.

The volume ratio of the conductive diamond constituting the powder catalyst layer is preferably 30% or more in order to reduce the electric resistance and increase the effective electrode area. Further, if the surface of the electrode is coated with a hydrophobic component such as a fluororesin, the substance to be treated can be easily captured, so that the reaction efficiency can be improved. In order to obtain good conductivity, it is indispensable to add trace amounts of elements having different valences, and the preferable content of boron or phosphorus is 1 to 100000 ppm, and the more preferable content is 100 to 10,000 ppm. Specific raw material compounds include boron oxide and diphosphorus pentoxide, which have low toxicity. DLN, a composite material with amorphous silicon oxide
(Diamond-like nano-composite) etc. can also be used.

Depending on the method of synthesizing diamond, a part of the non-diamond component is generated and may be contained in the diamond component. These non-diamond components and other non-corrosion resistant carbon components are consumed by being dissolved in the electrolytic solution and have little practical effect, but it is desirable to remove them by acid washing or the like before use. The diamond particles thus produced may be used as a normal electrode by supporting them on a substrate or a power feeding body as described above, but when used as a three-dimensional electrode in a fluidized bed or a fixed bed, the reaction area increases. The processing capacity is improved.

The material of the electrolytic cell and the spacer is organic.
Compound, and fluorinated if fluoride ion is used
From the viewpoint of durability and stability against substance ions, glass
Inning material, carbon, titanium, stainless steel, vinyl chloride
Nyl resin, polyethylene resin, polypropylene resin and
A PTFE resin or the like can be preferably used. diamond
Electrodes have much higher electrolysis voltage of water electrolysis than other electrodes,
Electric power consumption may be a problem. Improve this problem
For the purpose of forming a diamond on the substrate or current collector
After that, a catalyst may be further supported. As the anode catalyst, P
bO ₂, SnO₂And IrO₂As a cathode catalyst
Is platinum, RuO₂, Copper and iron. As cathode
Is platinum, conductive diamond, iridium, carbon
Etc. can be used. Ca and Mg ions deposited by electrolysis
When a reverse current is applied to remove precipitates containing
Is preferably stable against anodic polarization, so
Platinum, diamond and iridium are suitable.

The electrolysis condition is that the temperature is 5 to 40 ° C. and the current density is 0.01 to 10 when a normal electrode other than the three-dimensional electrode is used.
It is preferably A / dm ² . When electrodialysis is continued, alkali hydroxide or the like is generated in the cathode chamber, and calcium or magnesium hydroxide may be precipitated. Further, when the acidity of the anolyte becomes high (pH becomes low), hydrogen fluoride gas may be generated. To prevent these phenomena, the anolyte and the catholyte may be mixed to maintain the pH in the weakly acidic or neutral region of 3 or more.

The electrode for electrolysis containing the conductive diamond of the present invention as an electrode substance can be preferably used as an anode, but it may be used as a cathode and may be selected in consideration of cell voltage, price and the like.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an electrodialysis cell using the conductive diamond anode of the present invention will be described below with reference to the accompanying drawings, but the present invention is not limited thereto.

FIG. 1 is a schematic sectional view illustrating an electrodialysis tank according to the present invention. The box-shaped electrodialysis cell main body 1 includes a cation exchange membrane 2 and an anion exchange membrane 3 (three in the illustrated example) that are alternately located, and an anode chamber 4 at the left end and a cathode chamber 5 at the right end in the figure and It is divided into a total of three desalting chambers 6A and two concentrating chambers 6B between the two polar chambers. The desalting chamber and the concentrating chamber may be collectively referred to as an intermediate chamber. An anode 7 coated with conductive diamond as an electrode material is provided in the anode chamber 4.
However, in the cathode chamber 5, cathodes 8 made of platinum plates or the like are installed. Further, a porous spacer 9 is installed between each ion exchange membrane 2 and 3 and the electrodes 7 and 8 so as to prevent these from contacting each other and to control the flowing water to be uniform. Below the electrodialysis tank body 1, a horizontally extending cylindrical treated water supply pipe 10 is installed, and the treated water supply pipe 10 fluorinated into the desalination chamber 6A in the electrodialysis tank body 1. A connection pipe 11 for supplying water to be treated, which is waste water containing sodium or the like, is branched and connected to the corresponding bottom surface of the tank body 1. Further, a concentrated water circulation pipe 21 is installed in parallel with the untreated water supply pipe 10, and concentrated water from a concentrated water take-out pipe described later is circulated from the concentrated water circulation pipe 21 to the concentrating chamber 6B through a connecting pipe 23. .

An anolyte extraction pipe 12 is inserted into the anode chamber 4 so that the anolyte is taken out and supplied to the gas-liquid separator 13 for the anode chamber. An oxygen gas recovery pipe 14 and an anolyte recovery pipe 15 are connected to the gas-liquid separator 13. Further, a catholyte extraction pipe 16 is inserted into the cathode chamber 5 so that the catholyte is taken out and supplied to the gas-liquid separator 17 for the cathode chamber. A hydrogen gas recovery pipe 18 and a catholyte recovery pipe 19 are connected to the gas-liquid separator 17. A desalted water outlet 20 is formed on the upper surface of the desalination chamber 6A, and a concentrated water outlet 22 is formed on the upper surface of the concentration chamber 6B. In order to treat wastewater containing fluoride ions using the electrodialysis tank having such a configuration,
While energizing between the conductive diamond anode 7 and the platinum cathode 8, a waste water containing fluoride ions such as sodium fluoride is supplied to the treated water supply pipe 10, and the desalination chamber 6A is supplied through the connecting pipe 11.
The waste water is supplied to and the treated desalted water is collected from the desalted water outlet 20.

The water to be treated (drainage) in each desalting chamber 6A is placed in an electric field applied between both electrodes, and sodium ions, which are cations in the water to be treated, are drawn toward the cathode 8 to exchange cations. The concentrating chamber 6B and the cathode chamber 5 that are adjacent to each other through the membrane 2
Move to. On the other hand, the fluoride ions, which are anions in the water to be treated, are drawn toward the anode 7, pass through the anion exchange membrane 3 and move to the concentrating chamber 6B and the anode chamber 4 adjacent to each other. In the concentration chamber 6B, the electrolytic solution is concentrated by electrodialysis.
The concentrated water is supplied from the connecting pipe 23 to the concentrating chamber 6B, is discharged to the outside of the concentrating chamber 6B through the concentrated water outlet 22 and is partially recovered, and the rest is circulated to the concentrated water circulating pipe 21. The catholyte in the catholyte compartment 5 has a high concentration of sodium ions penetrating the cation-exchange membrane 2 to form sodium hydroxide and become alkaline. The hydrogen gas introduced into the gas-liquid separator 17 and gas-liquid separated by the gas-liquid separator 17 is taken out of the system through the hydrogen gas take-out pipe 18, and the sodium hydroxide aqueous solution is taken as a catholyte recovery pipe.
It is taken out of the system from 19. This aqueous sodium hydroxide solution may be supplied to the anode chamber 4 and used to maintain the pH of the anolyte solution at 3 or higher.

On the other hand, the anolyte in the anolyte compartment 4 has a high concentration of fluoride ions penetrating the anion exchange membrane 3 to generate hydrofluoric acid and become acidic.
From 12 to the anolyte gas-liquid separator 13, this gas-liquid separator
The oxygen gas that has been gas-liquid separated in 13 is taken out of the system through an oxygen gas take-out pipe 14, and the hydrofluoric acid aqueous solution is taken out of the system through an anolyte recovery pipe 15. Desalination chamber 6 by the electrodialysis treatment
The cation concentration and the anion concentration in the water to be treated in A become substantially zero and can be recovered as clear water. Also, a small amount of highly concentrated waste liquid in which the electrolytic solution is concentrated can be obtained from the concentrating chamber 6B. In this electrodialysis treatment, the anode chamber 4
Although a high concentration of hydrofluoric acid is generated, the use of a conductive diamond electrode having high resistance to fluoride ions as the anode 7 causes almost no wear and allows electrolytic treatment for a long time without replacement. I can continue.

Next, examples and comparative examples of the electrodialysis anode and the electrodialysis method using the same according to the present invention will be described, but these do not limit the present invention.

Example 1 The electrodialysis cell shown in FIG. 1 was assembled as follows. On both sides of a niobium plate with an electrode area of 200 cm ² and a thickness of 1 mm,
Diamond having a thickness of 10 μm and doped with 1500 ppm of boron was deposited by a hot filament CVD method to form an anode,
A 1 mm thick nickel plate plated with 1 μm of platinum was used as the cathode. CM manufactured by Asahi Glass Co., Ltd. as a cation exchange membrane
V, AMV manufactured by the same company was used as the anion exchange membrane.
Demineralization using a cell frame made of vinyl chloride resin, a spacer made of polypropylene net, a gasket made of Viton rubber, and the cation exchange membrane and anion exchange membrane except for the anode chamber and the cathode chamber at both ends. 6 chambers and 5 concentrating chambers
The cell was an electrodialysis cell consisting of a chamber. The distance between the cation exchange membrane and the anion exchange membrane was maintained at 2 mm.

A drainage solution containing 200 ppm of sodium fluoride
When supplied to 6 desalting chambers at a rate of 25 liters / hour, and electrodialyzed at room temperature with a current density of 0.5 A / dm ² , a concentration of sodium fluoride of 10000 ppm was obtained from the concentrating chamber at a current efficiency of about 60%. Was obtained at a rate of 0.5 l / h. The anolyte from which oxygen gas was separated was supplied to the lower part of the cathode chamber, and the catholyte from which hydrogen gas was separated was supplied to the anode chamber. No performance deterioration was observed even after 1000 hours of operation, and neither diamond wear nor corrosion of the cell frame was detected. The fluorine concentration in the desalted water was less than 50 ppm. The pH of each electrolysis chamber was maintained almost neutral.

Example 2 (acceleration test after Example 2) An electrode area of 2 cm ² was applied to both sides of a niobium plate having a thickness of 10 μm and 1500 p.
An electrode in which diamond doped with pm of boron was deposited by a hot filament CVD method was used as an anode, and a platinum plate was used as a cathode. A 3% aqueous sodium fluoride solution was prepared in a 1000 ml PTFE container, and the anode and cathode were immersed in the aqueous sodium fluoride solution to a current density of 3 A / dm ² , and the gap between the electrodes was adjusted to 50 mm at room temperature. After electrolysis with
The cell voltage was 4 V, and there was almost no change in voltage even after 8,000 hours of operation. When the anode was analyzed after the completion, the diamond was hardly consumed and no corrosion of the substrate was detected.

Example 3 An electrode area of 2 cm ² and a thickness of 1 mm on both sides of a niobium plate was applied with 10 μm.
An electrode in which diamond having a thickness of 10,000 and doped with boron of 10000 ppm was deposited by a hot filament CVD method was used as an anode, and a platinum plate was used as a cathode. A 3% aqueous solution of sodium fluoride was prepared in a 1000 ml PTFE container, and the anode and cathode were immersed in the aqueous solution of sodium fluoride to a current density of 30 A / dm ² , and the gap between the electrodes was adjusted to 50 mm, and 40 C Electrolysis was carried out at a cell voltage of 16 V, which was almost the same even after 2000 hours of operation. When the anode was analyzed after the completion, the diamond was found to be slightly consumed, and no corrosion of the substrate was detected.

Example 4 An electrode was prepared by depositing diamond having a thickness of 10 μm and doped with 10000 ppm of boron on a tantalum plate by a hot filament CVD method, and was used as an anode, and a platinum plate was used as a cathode. A 3% sodium fluoride aqueous solution was prepared in a 1000 ml container, and the anode and the cathode were immersed in the sodium fluoride aqueous solution at a current density of 30 A / dm ² and electrolysis was carried out at room temperature. The cell voltage was 20 V. The voltage was almost the same after 2000 hours of operation. When the anode was analyzed after the completion, the diamond was found to be slightly consumed, and no corrosion of the substrate was detected.

Comparative Example 1 Electrolysis was carried out in the same manner as in Example 2 except that a titanium plate plated with platinum having a thickness of 5 μm was used as an anode. The initial cell voltage was 8 V, but immediately after the start. From the result, weight consumption was observed, and most of the catalyst was eluted after 1000 hours, and titanium was dissolved in the base material, and electrolysis was disabled. Precipitation of platinum and titanium was detected in the solution.

Comparative Example 2 Electrolysis was performed in the same manner as in Example 3 except that a niobium plate plated with platinum having a thickness of 5 μm was used as an anode. The initial cell voltage was 14 V, but immediately after the start. From the result, weight consumption was observed, and most of the catalyst was eluted after 2000 hours, and the dissolution of the base material proceeded, so that the electrolysis became impossible. Precipitation of platinum and niobium was detected in the solution.

Comparative Example 3 Electrolysis was carried out in the same manner as in Example 3 except that a niobium plate having a 100 μm-thickness PbO ₂ plating on the entire surface was used as the anode, but the initial cell voltage was 15 V. Immediately after the start, the Pb component was consumed, and the Pb concentration in the electrolytic solution increased. The voltage after the lapse of 2000 hours was the same as the initial voltage, but the Pb concentration in the liquid became 5000 ppm, which left a problem for practical use. The solution turned brown as the electrolysis continued.

Comparative Example 4 Electrolysis was carried out in the same manner as in Example 2 except that a 100 μm-thick SnO ₂ plated copper plate was used as the anode. The initial cell voltage was 18 V, but immediately after the start. As a result, the Sn component was consumed, and the Sn concentration in the electrolytic solution increased. The voltage after the lapse of 2000 hours was the same as the initial voltage, but the Sn concentration in the liquid became 2000 ppm, and there was a practical problem.
The solution turned blue as the electrolysis continued.

Comparative Example 5 Electrolysis was performed in the same manner as in Example 3 except that a glassy carbon rod electrode having a diameter of 3 mm and an area of 5 cm ² was used as the anode. The initial cell voltage was 15 V, but Immediately after the start, the consumption of the electrode was remarkable, and the exposed part almost disappeared after 1000 hours. The peeled pieces of the electrode remained in the solution.

[0034]

The present invention is an electrode for electrolysis, which is characterized by containing conductive diamond as an electrode substance and used for electrodialysis. In electrodialysis, corrosive substances may infiltrate into the anode chamber and cathode chamber, resulting in a high concentration, and when using ferrite electrodes or carbon electrodes as in the past, the electrodes deteriorate and need replacement. was there. However, in the present invention, since highly corrosive conductive diamond is used as the electrode material, even if the electrode is used for electrodialysis treatment in which a high concentration of corrosive substance may exist, deterioration does not occur for a long time. Electrodialysis can be continued without replacement. Also, an electrodialysis tank equipped with the electrode has the same effect.

Further, when this electrodialysis tank is used for electrodialysis of the water to be treated containing fluoride ions, the conductive diamond anode exhibits resistance to the fluoride ions even if highly corrosive fluoride ions are present in high concentration. It has stable operation. If electrodialysis is performed while maintaining the anolyte at pH 3 or higher, generation of hydrogen fluoride gas can be suppressed. When the anolyte and the catholyte are mixed for a predetermined time after the start of energization, the above-mentioned generation of hydrogen fluoride gas can be suppressed and the precipitation of hydroxide in the cathode chamber can be prevented or the precipitation can be dissolved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating an electrodialysis tank according to the present invention.

[Explanation of symbols]

1 electrodialysis tank body 2 Cation exchange membrane 3 Anion exchange membrane 4 Anode chamber 5 Cathode chamber 6A desalination chamber 6B concentration room 7 Conductive diamond anode 8 Platinum cathode 9 Spacer 10 Treated water supply pipe

Continued front page    (72) Inventor Kuniaki Yamada             1145 Ishikawa, Fujisawa City, Kanagawa Prefecture F-term (reference) 4D006 GA18 JA42C KE15R KE16P                       KE18P KE18Q KE28P KE28Q                       MA13 MA14 PA01 PB08 PB28                 4D061 DA08 DB18 DC13 EA02 EA09                       EB01 EB04 EB13 EB28 EB29                       EB30 EB31 EB37 EB39 GA07                       GA12 GA15 GC12 GC15

Claims (5)

[Claims] 1. An electrode comprising electroconductive diamond as an electrode substance and used for electrodialysis. 2. An electrodialysis cell in which a cell body is divided into one or more intermediate chambers and an anode chamber and a cathode chamber at both ends using a cation exchange membrane and an anion exchange membrane, and conductive diamond is used as an electrode material. An electrodialysis tank characterized by using the electrode as an anode. 3. An electrodialysis tank whose main body is divided into one or more intermediate chambers and an anode chamber and a cathode chamber at both ends by using a cation exchange membrane and an anion exchange membrane, and which is to be treated containing fluoride ions. A method of supplying water and concentrating the fluoride by electrodialysis, wherein conductive diamond is used as an electrodialysis anode. 4. The method according to claim 3, wherein electrodialysis is performed while maintaining the anolyte at a pH of 3 or higher. 5. The method according to claim 3, wherein the anolyte and the catholyte are mixed for a predetermined time after the start of energization.